#div1{
    width: 20em;
    height: 10em;
    border: black solid;
    background-color: red;
}

/*相对定位*/
#div2{
    width: 20em;
    height: 10em;
    border: greenyellow dashed 1px;
    background-color: yellow;
    position: relative;
    left: 1em;
    top: 1em;
}

/*绝对定位*/
#div3{
    width: 20em;
    height: 10em;
    border: darkorange double;
    background-color: cyan;
    position: absolute;
    left: 1em;
    top: 1em;
}

.fixed-side{
    width: 20em;
    height: 10em;
    border: darkmagenta solid 1px;
    position: fixed;
    left: 30em;
    top: 10em;
}

.one,.two,.three{
    width: 1em;
    height: 30em;
    border: maroon solid 1px;
    margin-bottom: 1em;
    overflow: hidden;

    float: left;
}

.clf{
    clear: both;
}

.four{
    width: 30em;
    height: 2em;
    border: #000000 solid 1px;
    background-color: indigo;
    margin-bottom: 5em;
}



